I took my just built Ar15 out to the range today. I shot about 150 rounds through it dialing in the aimpoint ML2 and then just having fun. The target was at 50 yards. I noticed that 5 of the bullets keyholed the target or went sidewaysd through the target. My upper is a Larue DMR 16" stealth with 1:8 twist. I unfortunatly used 4 different types of ammo so I am unable to pinpoint if it was a ammo issue. Any help would be appriciated.

A 1:8 twist with 55 gr. bullets is a very marginal combination. It is a whole lot better than a 1:7 but still, a 1:8 is pretty fast for a 55 gr. bullet. A 55 should stabilize OK in a 1:8 but a 1:9 or 1:12 would be better, and with UMC being reportedly slightly under powered, my money lies with the UMC ammo being the culprit.

Join the N.R.A.Beware speaking with a sharp tongue as you are apt to cut your own throat.On the 8th day, God created HKs.NOT BigBore, who is owner of ADCO.

Originally Posted By Big-Bore:A 1:8 twist with 55 gr. bullets is a very marginal combination. It is a whole lot better than a 1:7 but still, a 1:8 is pretty fast for a 55 gr. bullet. A 55 should stabilize OK in a 1:8 but a 1:9 or 1:12 would be better, and with UMC being reportedly slightly under powered, my money lies with the UMC ammo being the culprit.

That is what I suspected also. I need to go back and be more specific with ammo during each 20 minute shooting session.

Double check the FS being loose, with possibly a loose FS that was causing bullet strikes to the FS, with and end result of a few tumbled rounds.

Short of that, funky ammo with some of the bullets a tad cross width under sized, barrel fouled with too much copper to cause the problem, or 5 stray rounds from another shooter.

So on that note, double check the FS to make sure it tight, has no bullet strike, and even check the amount of copper that you are pulling from the barrel rifling when using something like sweets bore solvent to see if the build up is abnormal for only 150 rounds (us did clean the barrel fully before shooting, correct?).

Originally Posted By Dano523:Double check the FS being loose, with possibly a loose FS that was causing bullet strikes to the FS, with and end result of a few tumbled rounds.

Short of that, funky ammo with some of the bullets a tad cross width under sized, barrel fouled with too much copper to cause the problem, or 5 stray rounds from another shooter.

So on that note, double check the FS to make sure it tight, has no bullet strike, and even check the amount of copper that you are pulling from the barrel rifling when using something like sweets bore solvent to see if the build up is abnormal for only 150 rounds (us did clean the barrel fully before shooting, correct?).

Originally Posted By Dano523:Double check the FS being loose, with possibly a loose FS that was causing bullet strikes to the FS, with and end result of a few tumbled rounds.

Short of that, funky ammo with some of the bullets a tad cross width under sized, barrel fouled with too much copper to cause the problem, or 5 stray rounds from another shooter.

So on that note, double check the FS to make sure it tight, has no bullet strike, and even check the amount of copper that you are pulling from the barrel rifling when using something like sweets bore solvent to see if the build up is abnormal for only 150 rounds (us did clean the barrel fully before shooting, correct?).

Originally Posted By Big-Bore:
A 1:8 twist with 55 gr. bullets is a very marginal combination. It is a whole lot better than a 1:7 but still, a 1:8 is pretty fast for a 55 gr. bullet. A 55 should stabilize OK in a 1:8 but a 1:9 or 1:12 would be better, and with UMC being reportedly slightly under powered, my money lies with the UMC ammo being the culprit.

That is what I suspected also. I need to go back and be more specific with ammo during each 20 minute shooting session.

First thing that popped into my mind also

I have never been a fan of Remington UMC

Also use more than one target, keep track of the rounds used with each target

Originally Posted By iNeXile556:55gr is just fine for 1:7, instability is from too slow a twist not too fast. I shoot 40-80gr from my 1:7 without a problem.

I would not say a 55 gr. bullet is "just fine for a 1:7" because all of my 1:7s do not shoot their best with anything less than 69 gr. Even the 1:8s do not like them all that much, preferring the midweights the best. My 1:7s shoot 55 gr. bullets within MOGrapefruit but they certainly do not shoot their best with the lighter bullets. But still you are correct, over stabilized bullets may not be as accurate as heavier bullets but it is under stabilized bullets that will tumble.

As far as ricochets off the ground. Could be. I have seen some pretty queer things happen from ricochets. Look in the last issue, the NV2011-04 match, issue of the Fifty Caliber Shooter's Associations VHP magazine. There is a picture of a bullet shot at a 1000 yard match that landed short, ricocheted off the ground and stuck in the target tip first like an arrow, not penetrating the target and the bullet was not deformed much at all. They cannot nickname the shooter Skip (already taken and retired) but they did suggest calling him "Stick."

Join the N.R.A.Beware speaking with a sharp tongue as you are apt to cut your own throat.On the 8th day, God created HKs.NOT BigBore, who is owner of ADCO.

It's either the flash hider, or there was a problem with the barrel, or, one of the ammo types in question is undersized. Remove the flash hider, then, one by one, fire a box of each ammo at a separate target. If only one ammo brand shows the problem, bingo. If they all do, it's the barrel.
If none do. Reinstall the F/H, and repeat the test. If they all do it. It's the flash hider. If one does it, it's that ammo.

55gr will shoot fine in any 1/7 twist. It is overly long bullets that have stabilization problems with 1/9-1/12 twist barrels. It's the length and not the weight, but since the heavier bullets are normally longer, weight is associated with the symptom. There are heavier, shorter bullets that stabilize in the slower twist barrels just fine. What you have with a fast twist like 1/7 is over stabilization. Normally this tends to cause a round to self destruct if it's construction is like that of a varmint round.

Originally Posted By Dano523:
Double check the FS being loose, with possibly a loose FS that was causing bullet strikes to the FS, with and end result of a few tumbled rounds.

Short of that, funky ammo with some of the bullets a tad cross width under sized, barrel fouled with too much copper to cause the problem, or 5 stray rounds from another shooter.

So on that note, double check the FS to make sure it tight, has no bullet strike, and even check the amount of copper that you are pulling from the barrel rifling when using something like sweets bore solvent to see if the build up is abnormal for only 150 rounds (us did clean the barrel fully before shooting, correct?).

I did not clean my new barrel before shooting.....Is that a problem?

It may or may not be causing the bullet tumbling but a new barrel/rifle should always be thoroughly cleaned before shooting. I'm not sure about Larue but most manufacturers use some sort of coating to protect the components from rusting while being stored and/or shipped and that will need to be cleaned out/off or it could cause you problems.

"....see in this world there's two kinds of people my friend ... those with loaded guns and those who dig ... you dig"

Originally Posted By iNeXile556:
55gr is just fine for 1:7, instability is from too slow a twist not too fast. I shoot 40-80gr from my 1:7 without a problem.

I would not say a 55 gr. bullet is "just fine for a 1:7" because all of my 1:7s do not shoot their best with anything less than 69 gr. Even the 1:8s do not like them all that much, preferring the midweights the best. My 1:7s shoot 55 gr. bullets within MOGrapefruit but they certainly do not shoot their best with the lighter bullets. But still you are correct, over stabilized bullets may not be as accurate as heavier bullets but it is under stabilized bullets that will tumble.

As far as ricochets off the ground. Could be. I have seen some pretty queer things happen from ricochets. Look in the last issue, the NV2011-04 match, issue of the Fifty Caliber Shooter's Associations VHP magazine. There is a picture of a bullet shot at a 1000 yard match that landed short, ricocheted off the ground and stuck in the target tip first like an arrow, not penetrating the target and the bullet was not deformed much at all. They cannot nickname the shooter Skip (already taken and retired) but they did suggest calling him "Stick."

Skip!

I agree about the light rounds not being optimum in the faster twist, but it will still stabilize and as you agreed, not keyhole.
I have had keyholes from ricochets on numerous occasions. I've even did the ricochet shots for fun, (my own range, no danger) try for 10 ring off the ground!. They can and do keyhole.

You can damn near aim ricochets off water.

The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it.

Originally Posted By pavlovwolf:It's either the flash hider, or there was a problem with the barrel, or, one of the ammo types in question is undersized. Remove the flash hider, then, one by one, fire a box of each ammo at a separate target. If only one ammo brand shows the problem, bingo. If they all do, it's the barrel.
If none do. Reinstall the F/H, and repeat the test. If they all do it. It's the flash hider. If one does it, it's that ammo.

55gr will shoot fine in any 1/7 twist. It is overly long bullets that have stabilization problems with 1/9-1/12 twist barrels. It's the length and not the weight, but since the heavier bullets are normally longer, weight is associated with the symptom. There are heavier, shorter bullets that stabilize in the slower twist barrels just fine. What you have with a fast twist like 1/7 is over stabilization. Normally this tends to cause a round to self destruct if it's construction is like that of a varmint round.

+1
I've never encountered a 1-7 that would not shoot 55gr OK. I do get key holing from longer (heavier) bullets in my 1-9 barrels.